Model Output Discussion 22/07/12 Onwards.

[Glacier Point]

The latest 500mb anom chart for the start of the final week of Aug continues to look very familiar...

Careful there, here's how CPC derived forecast from NAEFS looked for the current period:

Over the last two to three weeks, we've seen a very dynamical synoptic pressure pattern. Strong Azores ridge, retrogression, deep upper low (which somewhat failed to pack the same punch as they did in June), and now upper ridge, to be followed by... deep upper low in the Atlantic. I'm with TonyH on this one, pattern change since mid July.

Modelling is still stuck on how to evolve the upper low next week. I've noticed the ensemble mean tools are keen to develop the lows first, and then pick up the downstream ridge development after. This seems to be occuring again with a stepping up on the development of a mean ridge over Europe mid next week onwards. I suspect we might be overlooking the possibility of some very warm temperatures over Europe end of next week, and it wouldn't take much given the synoptic situation for those to work their way across the Channel.

[johnholmes]

if one looks at rather longer term teleconnections they all tend to support the mid term ideas shown by the 500mb anomaly charts-that is unsettled with little sign of any prolonged high pressure dominated type weather. The MJO and the AO and NAO(yes I know they are not drivers but simply general indicators of the pressure patterns) support the unsettled theme possibly into September. That is not to say there will not be decent days mixed in with less decent ones.

[Frosty.]

The latest models show a very unsettled spell next week, at least for a time around midweek with a low over the uk but the southeast could be favoured for some of the best weather at times with warm and dry spells between the rainbands and showers. The Gfs 06z starts with high pressure and ends with high pressure with a real mixed bag inbetween, a mix of warm and unsettled and cool and unsettled. The breakdown of the current fine spell is still on track for sunday but not a write off and some areas will remain warm and bright while others catch some showers but tomorrow looks very warm and fine for most of the BI but with some mist and low cloud to northeastern coasts as a SE'ly breeze develops but then a lot of rain spreading north and east during the first half of next week and gradually becoming cooler, but warm in the SE for a large chunk of next week.

PS. I'm going to clutch a straw and say there is an outside chance of high pressure building from the continent into the BI in around 8 days time but it's a long shot with not much ensemble support..yet

Edited August 10, 2012 by Frosty039

[johnholmes]

Careful there, here's how CPC derived forecast from NAEFS looked for the current period:

Over the last two to three weeks, we've seen a very dynamical synoptic pressure pattern. Strong Azores ridge, retrogression, deep upper low (which somewhat failed to pack the same punch as they did in June), and now upper ridge, to be followed by... deep upper low in the Atlantic. I'm with TonyH on this one, pattern change since mid July.

Modelling is still stuck on how to evolve the upper low next week. I've noticed the ensemble mean tools are keen to develop the lows first, and then pick up the downstream ridge development after. This seems to be occuring again with a stepping up on the development of a mean ridge over Europe mid next week onwards. I suspect we might be overlooking the possibility of some very warm temperatures over Europe end of next week, and it wouldn't take much given the synoptic situation for those to work their way across the Channel.

I would agree with much of those ideas Stewart and also with the pattern change. I remain mystified how folk can say we have not had a pattern change. I suspect it MAY be that the pattern change has not given days of settled hot sunshine. But pattern change there has been if one looks at the run of 500mb charts from May through to the end of July.

Edited August 10, 2012 by johnholmes

[Alex]

Careful there, here's how CPC derived forecast from NAEFS looked for the current period:

Over the last two to three weeks, we've seen a very dynamical synoptic pressure pattern. Strong Azores ridge, retrogression, deep upper low (which somewhat failed to pack the same punch as they did in June), and now upper ridge, to be followed by... deep upper low in the Atlantic. I'm with TonyH on this one, pattern change since mid July.

Modelling is still stuck on how to evolve the upper low next week. I've noticed the ensemble mean tools are keen to develop the lows first, and then pick up the downstream ridge development after. This seems to be occuring again with a stepping up on the development of a mean ridge over Europe mid next week onwards. I suspect we might be overlooking the possibility of some very warm temperatures over Europe end of next week, and it wouldn't take much given the synoptic situation for those to work their way across the Channel.

There has been some ensemble members going for a very warm spell developing from next weekend, as you say I don't think anything is secured yet - we have the possibility of that warmth being pushed north across the UK, last nights ECM run although unsettled showed the potential with 20c uppers making their way across the southeast.

[summer blizzard]

A potentially unstable outlook in my opinion which could easily swing to anonomously warm to cold and back again.

Looking at the USA we see a classic El Nino pattern with a +PNA and pretty amplified Jet Stream, the result of which is a -NAO (especially during summer when the thermal gradient is low). Now the unstable pattern i refer to comes into the fray now because on the one hand such a scenario can encourage pressure to build over Greenland and a subsequent Atlantic Ridge/northerly however on the other hand the scenario can also result in a slow moving trough near the Azores which corresponds to todays scenario with a ridge over the UK/Scandinavia and at this time of year that is a warm outlook.

Given the -PDO and -QBO i must lean towards the Atlantic Ridge scenario however if GLAMM can increase measureably then we could see the later scenario persist.

On the whole however i would suggest the outlook is drier and probably sunnier than average, it is the temperature which is up in the air.

[Frosty.]

A potentially unstable outlook in my opinion which could easily swing to anonomously warm to cold and back again.

Looking at the USA we see a classic El Nino pattern with a +PNA and pretty amplified Jet Stream, the result of which is a -NAO (especially during summer when the thermal gradient is low). Now the unstable pattern i refer to comes into the fray now because on the one hand such a scenario can encourage pressure to build over Greenland and a subsequent Atlantic Ridge/northerly however on the other hand the scenario can also result in a slow moving trough near the Azores which corresponds to todays scenario with a ridge over the UK/Scandinavia and at this time of year that is a warm outlook.

Given the -PDO and -QBO i must lean towards the Atlantic Ridge scenario however if GLAMM can increase measureably then we could see the later scenario persist.

On the whole however i would suggest the outlook is drier and probably sunnier than average, it is the temperature which is up in the air.

A very good post, hope your thoughts become reality. The models are looking disturbed next week with a lot of low pressure over or near the uk but I currently think the weather will improve again in the south and east beyond midweek with a classic nw/se split developing with hp to the se and lp to the northwest.

[summer blizzard]

A very good post, hope your thoughts become reality. The models are looking disturbed next week with a lot of low pressure over or near the uk but I currently think the weather will improve again in the south and east beyond midweek with a classic nw/se split developing with hp to the se and lp to the northwest.

I actually find the SE/NW scenario unlikely as that is typically the result of a strong zonal pattern which is not indicated. It is much more likely in my opinion that we will either see a mid-Atlantic ridge and northely or a UK/Scandinavian Ridge and high pressure.

[shedhead]

Careful there, here's how CPC derived forecast from NAEFS looked for the current period:

Over the last two to three weeks, we've seen a very dynamical synoptic pressure pattern. Strong Azores ridge, retrogression, deep upper low (which somewhat failed to pack the same punch as they did in June), and now upper ridge, to be followed by... deep upper low in the Atlantic. I'm with TonyH on this one, pattern change since mid July.

Modelling is still stuck on how to evolve the upper low next week. I've noticed the ensemble mean tools are keen to develop the lows first, and then pick up the downstream ridge development after. This seems to be occuring again with a stepping up on the development of a mean ridge over Europe mid next week onwards. I suspect we might be overlooking the possibility of some very warm temperatures over Europe end of next week, and it wouldn't take much given the synoptic situation for those to work their way across the Channel.

I don't think anyone has overlooked the possiblity of European heat drifting our way later next week, but given all I can currently see a possibility is all it remains, with the odds favouring generally mixed conditions in a typical NW/SE set up.

[Frosty.]

I actually find the SE/NW scenario unlikely as that is typically the result of a strong zonal pattern which is not indicated. It is much more likely in my opinion that we will either see a mid-Atlantic ridge and northely or a UK/Scandinavian Ridge and high pressure.

Yes the mid atlantic ridge idea has been showing on recent gfs runs later in FI, I think the 6z showed it with the azores high building across the uk at the end, temps look up and down in next few weeks, starting very warm then trending cooler, warming up again but possibly cyclonic and then cooler northerly with mid atlantic ridge or the uk/scandi ridge and high pressure as you say.

Edited August 10, 2012 by Frosty039

[Methuselah]

I would agree with much of those ideas Stewart and also with the pattern change. I remain mystified how folk can say we have not had a pattern change. I suspect it MAY be that the pattern change has not given days of settled hot sunshine. But pattern change there has been if one looks at the run of 500mb charts from May through to the end of July.

Agreed John...Just by extrapolating the last four weeks' weather backwards, throughout May, June and July, makes that abundantly clear IMO? Indeed, if we'd had the present pattern throughout the summer, no one would be looking for reasons for the dire weather!

[MP-R]

Well the models certainly paint an interesting picture failing a summery one. The GFS definietly brings in a return to unsettled conditions from Monday onwards but with the low responsible shrinking and isobars becoming fewer by Friday, there is a possibility of another warm weekend next weekend albeit not as nice as this current spell.

Although the underlying theme of unsettled continues as has been the case all summer, the theme within that is that temperatures should be on the warm side for most time, average at worst, and the emphasis is one convective rainfall and thunderstorms rather than dull dreary frontal rainbands as was the case through a lot of June and the first two thirds of July.

[phil nw.]

Some interesting posts today on the possible outlook.

The 00z Ens.Graph would indicate something cooler and unsettled after the weekend for around 5 days before drying out in week 2 with temperatures more around average.

Here is the London Ens.

http://www.weatherca...e-forecast.html

The Ens means still show the jetstream very much on our latitude-although more fragmented.The advancing Atlantic trough is modelled around the north and west of the UK through much of next week thus the unsettled and cooler theme.

MJO is now in a more active state in phase 8 and it`s composite compares close to next weeks sypnotic modelling.

The south east quadrant again looks favoured for less rain and more sun and warmth which may well become more noticeable as thicknesses rise from the south again towards next week end.

Last nights NOAA site indicated low confidence in the 500hPa anoml outlook beyond day 8 so i think we may well see some different solutions for a few runs for the period beyond next week.

I certainly agree re.a pattern change since mid-July-that persistent Scandi/NW Euro trough long gone.

[shedhead]

I really don't see the need for members to keep reiterating almost run afer run that things are not as bad as in June, I think we know that. Also it'd fair to say that IF the weather of the last 3 or 4 weeks was indicative of the weather across the summer in general very few would be moaning about... but alas it isn't.

The 12 GFS does not back away from it's hitherto unsettled theme for later next week, indeed this T+144hrs chart, whilst not dog ugly, would not win any beauty contests either.

Certainly no sign of continental heat buiding north into the UK on the above chart (in fact it hasn't even built into Europe), but come early FI there are hints that this evolution could start to unfold.

That said the chart below, IF it were to verify, again has a rather temporary look about it.

Edited August 10, 2012 by shedhead

[SP1986]

I think I will be able to test a little theory of mine, that despite the mid level (850hPa) air being relatively warm, if the trough at 500hPa pools deep falling air (the green shades of the chart), the wind will be much much colder than the air temperature at the surface suggests. Therefore it could be 20C at the surface but feel like 13C due to winds percolating through the lower layers of the atmosphere, the distribution of air layers having a factor.. or rather the way the air layers are distributed.

So if this is the case, next week could feel very cool at times, despite actually not being that cool on paper.

[mushymanrob]

I would agree with much of those ideas Stewart and also with the pattern change. I remain mystified how folk can say we have not had a pattern change. I suspect it MAY be that the pattern change has not given days of settled hot sunshine. But pattern change there has been if one looks at the run of 500mb charts from May through to the end of July.

maybe its because we have swapped one changeable pattern for another one!

[reef]

I think I will be able to test a little theory of mine, that despite the mid level (850hPa) air being relatively warm, if the trough at 500hPa pools deep falling air (the green shades of the chart), the wind will be much much colder than the air temperature at the surface suggests. Therefore it could be 20C at the surface but feel like 13C due to winds percolating through the lower layers of the atmosphere, the distribution of air layers having a factor.. or rather the way the air layers are distributed.

So if this is the case, next week could feel very cool at times, despite actually not being that cool on paper.

The colours on the 500hPa charts arent directly related to temperatures but show the thickness of the air. How it feels on the ground is generally dictated by solar input at this time of the year, the effect of mixing air through layers of the atmosphere is generally minor. The thicknesses shown on the charts you mention are essentially the distance in the atmosphere between where the air pressure is 500hPa and 1000hPa. In low thickesses the distance is less (and often the temperature gradiant tighter) and vice versa when thicknesses are higher. As can be seen in spring, it can be -5C at 850hPa level and 12-15C at ground level, but only when a shower arrives does solar input cease and it actually feel cool at the surface.

[Frosty.]

The Gfs 12z operational run shows a warm but showery start to next week but then with a much cooler and more unsettled spell around the middle of next week, (at least for central and northern britain) but then quickly warming up again when the low moves away northeast and by the end of the week it could be very warm or hot again in southeastern parts of england and warm elsewhere but then further into FI it shows temps will fall away to below the seasonal average with 13-18c max from north to south, hopefully the ecm will show something different!

Edited August 10, 2012 by Frosty039

[Milhouse]

Some decent upper temperatures edging back northwards for next weekend. At this range we have seen things go either way. It could be upgraded into a more prolonged hot spell or it could be wiped off altogether.

[BLAST FROM THE PAST]

Here is a feature i'm looking at. Could this lead to jet diving into france and a -ve tilt. Plenty to watch for but from mid month this is first model idea that suggests possibility

BFTP

[Frosty.]

The Ecmwf 12z is looking pretty unsettled next week, low pressure swinging in from the southwest by midweek or sooner and then a very unsettled and much cooler few days with lots of rain and very breezy conditions, more like autumn than summer really. The ecm then shows a brief lull in the poor weather as the first low moves away but then is replaced by another trough moving northeast, then ending with a much cooler northerly poised to spread south. At least the warmth looks like lingering for the early part of next week but as the high moves further away and the low moves closer, it looks increasingly unsettled and then with a dartboard low over the north it looks dire, good weather for ducks though.

[Nick F]

Looking rather wet at times next week, particularly on Wednesday - 12z ECM precipitation charts:

Atlantic shortwave troughs ejecting NE on the forward side of the upper low/trough to the west of the Uk early/mid week engage warm and rather moist Tm airmass advecting up from the south - so certainly need to keep any eye on the potential for some torrential rainfall events.

[shedhead]

Indeed Nick, ECM paints a very unsettled picture, but it has been on the extreme end of things several times this Summer and should be viewed with a least a degree of sceptisism imo. That said the 18GFS is hardly inspiring and looks a fair way away from providing any imported heat.... at least yet!

Edited August 10, 2012 by shedhead

[Bobby]

Could be a lot of rain on the way next week

Good agreement for an unsettled wet/very wet spell of weather, especically in the N and W. Almost checkmate for this summer now with regards to a sustianed warm spell.

September can still deliver summery weather though of course.

[Bristawl Si]

There's been more than enough dire predictions on here in last two weeks, which haven' t really materialised so i'll take the latest with a warehouse load of salt.

Not the best summer outlook, granted, but no June/1st half of July that's for certain.